Elastomeric ethylene-propylene non-conjugated diene terpolymer ("EPDM") and isobutylene-conjugated diene copolymer ("butyl rubber") compositions are well known in the art.
Moreover, the use of EPDM and butyl rubber compositions as a material of construction for roof sheeting is also well known in the art.
Such sheeting provides, in the cured or crosslinked state, an excellent material for use on a roof in those applications where planar sheet material is either desirable or otherwise acceptable for disposition on (i.e. for purposes of being applied onto) substantially flat or moderately contoured roofing structures.
However, when the crosslinked EPDM or butyl rubber sheeting of the prior art is laid out onto certain intricately contoured surfaces of a portion of roof, such as a parapet, a chimney, a ventilator section or the like, the substantially planar or generally flat crosslinked sheeting material of the prior art is often deemed not acceptable for the intended use. The reason is because the crosslinked EPDM or butyl rubber sheeting materials of the prior art lack the "formability" characteristics or physical properties needed to successfully and permanently bond to (i.e. adheringly conform with and desirably cover) the surface countours of an irregularly shaped substrate.
Roofing material that is used to follow irregular contours is known as flashing. Crosslinked EPDM or butyl rubber roof sheeting materials are not normally used as flashing because gaps are known to readily develop around roofing contours, between the sheeting section of a roof and other portions of the roof where the EPDM or butyl rubber is used as flashing.
While crosslinked EPDM and butyl rubber sheeting materials have each established an excellent reputation as an effective barrier to roof leaks for those substantially flat or moderately contoured surfaces upon which they are applied, nevertheless, such leak-protection has not been available to those portions of the roof which are characterized by their irregular shape. Thus, the excellent protection afforded by EPDM or butyl rubber compositions has not been available as flashing. This results in the general inability to protect those sections of the roof characterized by irregular shape against leakage. The utilization of EPDM or butyl rubber roof sheeting, a most effective long-term protector against water leakage, is seriously compromised by this defect in cured EPDM and butyl rubber.
As was noted above, the use of EPDM compositions as a material of construction for roof sheeting is well known in the art. Also, EPDM compositions containing accelerator-vulcanizer blends for in situ curing of roof sheeting and flashing is known--as is disclosed, e.g., in U.S. Pat. No. 4,461,875 (in the name of Crepeau).
U.S. Pat. No. 3,531,444 (in the name of Behrens) describes a vulcanizable composition that is said to include sulfur, zinc oxide, a sulfur vulcanizable hydrocarbon elastomer (such as butyl rubber), and a vulcanization accelerator composition. The vulcanization accelerator composition is said to include a combination of a bis(morpholinothiocarbonyl) sulfide of specified structure as well as either thiuramsulfide or a metal dithiocarbamate.
U.S. Pat. No. 3,644,304 (also in the name of Behrens) is directed to a vulcanizable composition that is said to include a diene modified ethylene-propylene elastomer, copper 2-mercaptobenzothiazole and either thiuram sulfide or a metal dithiocarbamate.
U.S. Pat. No. 3,897,405 (in the name of Son et al.) is directed to EPDM polymers grafted with vulcanization accelerators. This patent, more particularly, discloses the preparation of EPDM polymers having grafted thereon vulcanization accelerators and polymer blends with highly unsaturated diene rubbers that are cured using sulfur.
Another reference of interest is U.S. Pat. No. 4,012,332 (also in the name of Behrens) which discloses an accelerator composition for the vulcanization of diene elastomers, comprising a benzothiazole sulfenamide, a thiuram sulfide, and copper 2-mercaptobenzothiazole.
The lack of elasticity of uncured EPDM in addition to its favorable characteristics of excellent weatherability, low temperature flexibility, and resistance to direct sunlight lends itself for use as roof flashing.
Once the uncured EPDM roof sheeting and flashing are installed, it is desirable that the ambient cure takes place as soon as possible so as to develop desirable physical properties similar to vulcanized roof membrane.
Surprisingly, it has been found that certain dialkylthioureas, when utilized as the primary accelerator in curative tri-blends, show faster self-cure at ambient temperatures than known blends containing dipentaethylenethiuram hexasulfide ("DPTH") as the primary accelerator, as taught in the above-noted U.S. Pat. No. 4,461,875 as well as in U.S. Pat. Nos. 4,514,442 and 4,666,785 (both in the name of Crepeau).